Testing of vehicle lighting is an important aspect of vehicle inspection. It has become standard in a number of situations to inspect vehicle lighting, and, of course, proper operation of a vehicle's lights can be crucial for safety purposes in the course of operation of the vehicles. Thus, in many states, it is now common practice to require periodic inspection of lighting systems of trucks, cars, airplanes and other vehicles.
The problem of ensuring proper vehicle lighting operation is particularly acute in the trucking industry because of the high mileage involved and the practice of frequently switching freight traiers from one tractor to another. Generally, a large number of such freight trailers will be located in pools at shipping points (e.g. railway yards, etc.) to be connected to an available tractor. In such situations, it is common practice to send a mechanic to these locations to inspect and repair the freight equipment. Inspection of the trailer's lights is part of this inspection to ensure that the trailer's lighting system will properly operate when it is connected to the tractor's lighting system by a suitable connector.
In the past, it has been common practice to use a spare tractor at the lot to connect to each of the trailers being tested in turn. With such a spare tractor, if only a single mechanic is making the inspection, it will be necessary for him to make two trips around the trailer. Specifically, the typical testing procedure begins with the mechanic first turning on one turn signal and the taillights and marker lights at the tractor. The mechanic will then go to the back of the trailer to check these lights. Following this, he must return to the tractor to switch to the other turn signal and to apply the brakes for checking the stop lights. The mechanic must then go to the back of the trailer again to check these other lights. It should be noted that most trailers combine taillights with other functions by using dual-filament bulbs. Therefore, in addition to having to check both turn signal indicators separately, the two trips are also required to ascertain that both of the filaments are lit and that the wiring is not reversed.
Of course, the testing can be accomplished more easily if two operators are present for testing. In that case, one will remain in the tractor to control the lights while the other checks the trailer lighting operation from the back. However, this is normally undesirable since it requires allocating two men to do the job.
As noted above, the use of the spare tractor has a number of disadvantages. Either two testing operators are required, or a single testing operator must make two trips around each trailer. This requires a single mechanic to walk an extra mile for every 35 trailers checked (calculated using standard 48-foot trailer) due to the extra trip required around each trailer. When one combines this extra walking with the fatigue involved in climbing in and out of the tractor repeatedly, it becomes a significan factor in reducing the efficiency of the mechanic.
In addition, the use of an extra tractor has a number of other disadvantages. For example, it is difficult, timeconsuming and dangerous both to people and equipment to move a tractor around a crowded trailer lot to connect it to one trailer after the other. It is also expensive to operate the tractor, and runs down the battery of the tractor. A low battery in the tractor, or some other problem with the lighting system of the tractor, might be mistaken for a trailer lighting system problem. And, of course, if the tractor is being used for testing trailers, it will not be available for use on the road. Considering the costs of tractors, this latter point can be a significant disadvantage. Finally, it is necessary that the person doing the testing be qualified for driving the tractor, particularly considering the tight quarters that it is usually necessary to operate in on a crowded freight trailer lot.
Because of these difficulties, portable systems have been developed for checking the trailer lights without the need for connecting a tractor. U.S. Pat. No. 3,103,808 to Eichelberger and U.S. Pat. No. 3,737,767 to Slutsky are examples of such systems. In both of these systems, the testers are connected to the socket of the trailer where the tractor plug would normally be inserted. The tester contains switches which allow the operator to individually operate the various trailer lights.
In using the portable testing systems of U.S. Pat. Nos. 3,103,808 and 3,737,767, substantially the same testing procedure is used as in the case of a spare tractor. In other words, the mechanic will turn on one turn signal, the taillights and the marker lights at the front of the trailer where the light input socket is located, and then go to the back of the trailer to check these. Subsequently, he will return to the front of the trailer to switch to the other turn signal and the braking lights and then go back to the trailer again to check these other lights. In short, even with such portable testers, two trips around the trailer are required.
In addition to the disadvantage of extra walking, these previous testers do not provide a safe enclosure for the testing battery. Thus, a safety hazard exists for acid spills from the exposed battery. Also, the systems do not include an arrangement fo stopping the testing operation if the testing battery is low. Therefore, a low battery might be mistaken for an improperly operating trailer light.
Accordingly, although the portable testers disclosed in U.S. Pat. Nos. 3,103,808 and 3,737,767 represent a definite improvement over the use of a spare tractor, they still have certain drawbacks.